linux-kernel - Re: [PATCH 1/9] sysfs: add sysfs_remove_bin_file

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Date:   Thu, 7 Oct 2021 08:12:37 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Zev Weiss <zev@...ilderbeest.net>
Cc:     openbmc@...ts.ozlabs.org, Jeremy Kerr <jk@...econstruct.com.au>,
        Joel Stanley <joel@....id.au>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/9] sysfs: add sysfs_remove_bin_file_self() function

On Wed, Oct 06, 2021 at 10:58:59PM -0700, Zev Weiss wrote:
> On Wed, Oct 06, 2021 at 10:23:33PM PDT, Greg Kroah-Hartman wrote:
> > On Wed, Oct 06, 2021 at 05:09:46PM -0700, Zev Weiss wrote:
> > > This is simply the bin_attribute analog to sysfs_remove_file_self().
> > 
> > No, no binary sysfs file should be triggering a remove.
> > 
> > binary sysfs files are "pass-through-only" from userspace to hardware,
> > the kernel should not be even knowing what is read/written to them.
> > 
> > What do you think this is needed for?
> > 
> 
> So, I initially set out to be able to activate/deactivate specific DT nodes
> at runtime by using the device-tree "reserved" status as defined in the spec
> (but not currently used anywhere in the kernel) to mean essentially "create
> a device for this but don't bind a driver to it" (leaving it to userspace to
> invoke bind/unbind or similar), and added initial support for the specific
> driver I'm concerned with at the moment (aspeed-smc) -- that was the
> previous patch series linked in the cover letter of this one.
> 
> In the discussion of that series, Rob suggested as an alternate approach:
> 
> > Another possibility is making 'status' writeable from userspace. It is
> > just a sysfs file.
> 
> That seemed sort of appealing to me, and this seemed like the most obvious
> way to go about implementing it.  Given that DT properties are binary
> attributes, I gather you'd consider that a non-starter though?

Why would a text attribute of "status" be a binary sysfs file?  That
feels really wrong as again, binary sysfs files are not supposed to be
parsed or handled by the kernel at all, they are only a pass-through.

thanks,

greg k-h